For those that are interested and do not have access to searchable data bases:
Here are some citations to recent scientific studies backing up the need to control the feral cat populations.
IMPACT ON WILDLIFE
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Predation of wildlife by domestic cats Felis catus in Great Britain MICHAEL WOODS, ROBBIE A. MCDONALD, STEPHEN HARRIS Mammal Review Volume 33, Issue 2, Page 174-188, Jun 2003
Here is the abstract from the article. I thought the entire thing was interesting.
1. A questionnaire survey of the numbers of animals brought home by domestic cats Felis catus was conducted between 1 April and 31 August 1997. A total of 14 370 prey items were brought home by 986 cats living in 618 households. Mammals made up 69% of the items, birds 24%, amphibians 4%, reptiles 1%, fish < 1%, invertebrates 1% and unidentified items 1%. A minimum of 44 species of wild bird, 20 species of wild mammal, four species of reptile and three species of amphibian were recorded.
2. Of a sample of 696 individual cats, 634 (91%) brought home at least one item and the back-transformed mean number of items brought home was 11.3 (95% CI 10.4-12.2). The back-transformed means and number of cats retrieving at least one item from each prey group were: 8.1 (7.4-8.9) mammals for 547 (79%) cats, 4.1 (3.8-4.5) birds for 506 (73%) cats, 2.6 (2.2-3.0) herpetofauna for 145 (21%) cats and 2.2 (1.8-2.7) other items for 98 (14%) cats.
3. The number of birds and herpetofauna brought home per cat was significantly lower in households that provided food for birds. The number of bird species brought home was greater in households providing bird food. The number of birds and herpetofauna brought home per cat was negatively related to the age and condition of the cat. The number of mammals brought home per cat was significantly lower when cats were equipped with bells and when they were kept indoors at night. The number of herpetofauna brought home was significantly greater when cats were kept in at night.
4. Based on the proportion of cats bringing home at least one prey item and the back-transformed means, a British population of approximately 9 million cats was estimated to have brought home in the order of 92 (85-100) million prey items in the period of this survey, including 57 (52-63) million mammals, 27 (25-29) million birds and 5 (4-6) million reptiles and amphibians.
5. An experimental approach should be taken to investigate the factors found by this descriptive survey to influence the numbers of prey brought home by cats. In particular, investigation of potential management practices that could reduce the numbers of wild animals killed and brought home by cats will be useful for wildlife conservation, particularly in suburban areas.
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A Review of Feral Cat Eradication on Islands MANUEL NOGALES, AURELIO MARTÃN, BERNIE R. TERSHY, C. JOSH DONLAN, DICK VEITCH, NÉSTOR PUERTA, BILL WOOD, JESÚS ALONSO Conservation Biology Volume 18, Issue 2, Page 310-319, Apr 2004
Here is a quote from this article:
"Feral cats are directly responsible for a large percentage of global extinctions..."
They then go one to review methods of eradication.
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Cats protecting birds: modelling the mesopredator release effect, Franck Courchamp, Michel Langlais, George Sugihara Journal of Animal Ecology
Volume 68, Issue 2, Page 282-292, Mar 1999
Interestly enough this study shows that in areas with a high concentration of rats, cats will actually benefit the birds more by preying upon these rats (which eat eggs and unfledged young) than they hurt them by preying upon the birds. This is corroborated by the previous study that showed that cats ate 3 times more mammals than they did birds.
Again, here is the abstract:
1. Introduced predators account for a large part of the extinction of endemic insular species, which constitutes a major component of the loss of biodiversity among vertebrates. Eradication of alien predators from these ecosystems is often considered the best solution.
2. In some ecosystems, however, it can generate a greater threat for endemic prey through what is called the 'mesopredator release'. This process predicts that, once superpredators are suppressed, a burst of mesopredators may follow which leads their shared prey to extinction.
3. This process is studied through a mathematical model describing a three species system (prey-mesopredator-superpredator). Analysis of the model, with and without control of meso- and superpredators, shows that this process does indeed exist and can drive shared prey to rapid extinction.
4. This work emphasizes that, although counter-intuitive, eradication of introduced superpredators, such as feral domestic cats, is not always the best solution to protect endemic prey when introduced mesopredators, such as rats, are also present.
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DISEASE
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Helminth Parasites of the House Cat, Felis catus, in Connecticut, U.S.A. Rembiesa, Cheryl, Richardson, Dennis J. 2003: Comparative Parasitology: Vol. 70, No. 2, pp. 115–119.
In this study they conclude that controlling feral cat populations will reduce the occurance of parasites being transmitted to humans and domestic cats.
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I've run out of time, but you get the idea. I hope this helps your decision.
Kilgor